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O. A. COLBY.

ELECTRIC TOOL TEMPERING FURNACE.

APPLICATION HLED lllAY 4. i920.

Patented Oct. 31, 1922.

Ora ACo/fi BY ArrdRNEY' --30 solid blocks of refractory Patented Oct. 31, 1922.

STATES PA'F ENT pp gg us a. COLBY, os iawin, PENNSYLVANIA, ASSIGNOR TO was'rxns'n oosa ELECTRIC '&

inaNUFAcTUBINo COMPANY,

A CORPORATION or PENNSYLVANIA.

*' ELECTRIC 'rooL-rnmranrzqe roanscn- Application filed Mar 4, 1920. Serial 0.378190. 1w

To all whom it may concern: Beit knownrthat L-Ona A- COLBY, a citizen oflthe United States, and. a resident of Irwin, in the county of Westmoreland and 6'5 Stateofilennsylvanimhave invented a new andiruseful' Improvement in.-Electric Tool- Tempering F urnac'es, of which the following is =a specifications "My-invention relates to electric furnaces and particular1y to furnaces of the electricresistance; typepand it ihas fori one of its. objectsitorprovide afurnace whieh,may be operated continuously for comparatively long 'periods'of. time-at a relatively high temperature for tempering steel dies andfor heating and heat-treating metals. v Another object of my invention is to pro- :vide afurnace resistor which .shall have a .r'elativelydow. rate of deterioration and 'whichu'nay .beueasilyaand quickly replaced tincasezzitbecomes -damaged during the operation of the furnace.

Another/object of :my invention is to pro- .videfmeans for sim'ultaneously heating both sidesof metal dies placed in'a furnace of the above-designated character; y i'zln practicing nay-invention. .I provide a 'chamber in arefractory casing, the chamber having an arched'froof, resistorscomprising electrical-conduct- :ing material located :adjacent to the sides iof the'chamber and other resistor blocks located in the floor. of the chamber. I-provide .wells or hoppers in the casing adjacent to 85 the ends of the resistor. blocks andi-place therein a mass of electrical-conducting gran- ?ular'material which is adapted to conduct thecurrent to and from terminal electrodes -which project. into the wells.

)1 m Referring to the single sheet of drawings,

i Figure 1 is a top plan view of a furnace embodying my invention; Fig. 2 is a cross-sectional view of the same furnace along the line 11-11 of Fig. 1 and Fig. 3 is a crosssectional view of the furnace along the lines III'-III of Fig. 2.

The supporting structure of the furnace comprises an exterior metal casing or frame 1 in which is placed an outer shell '2 of heatinsulating brick and an inner shell 3 of lire brick. The tire brick 3 are spaced apart to rovide a chamber 4 substantially in the middle of the furnace. the chamber being provided with an arched rool 5 made of suitable liighly-refractory material adapted to withstand high temperatures.

.A main resistor ficomprises bricks or slabs of. refractory electrical conducting material, such as carborundum or silicon carbid, each brick having, a ,csubst antially rectangular cross section...- Each of the. -two, resistor blocks fi pisr located in a *substantiallv -V- shaped. trough 7r'formed' in the shell 3, its larger facebeing. so located :aszto' radiate heat aga nst ,the concave surface ofthe roof from which the .heat will be ,reflected downwardlynpon the material to heat treated.

plurality ofsblocks8 of resistance ma- 1.911511, s milar to theresistor blocks .6 butof somewhat smaller cross-sectional area, are located'in thefloor of the chamber 4, being held; ,in theirpropen operative position by suitable spacing n'iemberS .Which may consist of lire brick similar to that .used in the inner shell 3.. While I have shown the resistors 8 as projecting above the floor of the chamber 4,1 do not desire-to be limited to this arrangement and may locate these resistors beneath the. floor ,otthe chamber or level therewith so that the :resistors themselvesneed not carry thehweight of the material being heat treated.

" Opposite to, and ad'acent end of the 'resistor blocks (hand 8, the inner shell 3 is so spaced apart as to provide wells or hoppers 10 and 11 into which the ends ofthe resistor blocks extend. Terminal electrodes-1,2 extend from the outside oi the, furnace into the hoppers or wells 1] substantially at-the lower end thereof. .Each of the wells 10 and '11 is filledwith a mass 13 ofelectrical-conducting granular material, such as graphite .or coke, and this mass serves to conduct the vcurrent f-romthe terminal electrode, which may bemade of solid carbonaceous material. to the ends of the resistor blocks and in the case of the well 10, to conduct the current from one set of resistor blocks to the other. In Fig. 1, I have shown an arrangement of terminal electrodes and hoppers which will permit the electric supply-circuit conductors 14 bein located at the rear of the furnace out of the way of the operator.

One of the problems in connection with the use of solid refractory electrical-conducting material for resistors is that of a satisfactory connection to said resistors. As some oxidation of carborundum resistor blocks with the spirit and scope always occurs during the operation of the furnace, the resistor blocks will be gradually consumed, and unless some simple means is used to maintain the contact therewith, serious arcing will occur. The use of the granular electrical-conducting material 13 tends to prevent such arcing and provides a multitude of current paths by which the current may enter the resistor. Some oxidation of this granular material takes place during the operation of the furnace and, as the wells 10 and 11 are open at the top of the furnace, this material maybe easily tamped in place to provide good operative contact projecting ends of the resistor blocks and a fresh supply of such material may be easily added, as required.

am aware that an arched roof has already been used in the furnace art to reflect the rays from a resistor located in proximity thereto, butI believe it to be new to use solid refractory material of such formand cross-section that the larger area thereof may be located in heat-radiating relation to the arched roof which then reflects the rays upon the floor of the chamber to heat the same prior to the insertion'of the metal die to be tempered or radiates the heat upon the metal die itself. I believe it to be also new to provide an auxiliary resistor located in the fioor of the chamber to furnish heat to the lower side of the metal die when the same is placed in the chamber as, of course, the floor of the chamber is precluded from receivin any radiated heat as soon as a metal die 0 relatively large area is placed in the chamber to be heat treated.

While I have shown a specific embodiment of my invention, various changes may be made therein without departing from the of my invention and I desire, therefore, that only such limitations shall be placed thereon as are imposed by the prior art or are specifically set forth in the appended claims.

claim as my invention:

1. In an electric furnace, the combination with a. chamber and a concave roof for said chamber, of a plurality of resistors comprising solid blocks of refractory electricalconducting material of rectangular crosssection, one of the larger faces of said blocks being so located as to radiate heat against said concave roof, a plurality of hoppers at the rear of said furnace opposite the rear ends of said resistor blocks, a hopper at the front of said furnace opposite the front ends of said resistor blocks, solid terminal electrodes in said hoppers at the rear of said furnace-and a mass of electrical-conducting 60 granular material in said rear hoppers interposed between said electrodesf'and said resistors and adapted to conduct the current therebetween'andto prevent overheating of said electrodes, and'a mass of electrical conducting granular material in said front ho per adapted to conduct current between sald resistors.

2. In an electric-furnace, the combination with a chamber and a concave roof for said chamber, of a main resistor comprising solid blocks of electrical conducting material of rectan lar cross-section located at the sides of sai izhamberfone of the largeri facesof said hlocks'being: so located faSJ to radiate heat against said r0013 an autn'lianvresistor comprisingsolid' blocks of-electricaleconducting refractory material locatedatthe bottom of said chamber, hoppersfudjaoent the ends of said resistors, electl'ddesrtin said hop persand a =mam :of electrical-conducting granular material in said choppers-interposed between :said "electrodes and said iresistors, the cross-section ofsaid m'iisscbf'material being greater than the '5 crossrsection of the resistors toz-prevento erheating said electrodes. i v wise 3. In an electrie'furnace; the-combination with a chamher'and a concave rbofifor' said chamber, of a main'rresis'tonco blocks of"refractory electrics, con 'uctin'g material located at thesidescf saidichamher and adapted toheat;one siderof aniobject placed in said chambei' by'hmtzreflected from said roof, and comprising solidblocks 'of refraotdry'lelectrical-conducting material "LIOCBitGd'. in l'the floor of said chamber and ada ted tosuppo'rt an object placed in said cham r. and-,toheat the under side-thereof.

4. In an electric furnace; the combination with a chamberand a concave :roof for said chamber, of a main resistor. comprising solid blocks of refractory eIectricaLconducting material located at the sides of said chamber and adapted to heat one side of an object placed in said chamber by heat :reflected from said roof, hoppers located 0 positethe ends of said blocks, and a. masso electricalconducting pers adapted to conduct current from and to said resistor blocks and of :greater crosssection than said resistor blocks'to prevent overheating of said masses.

In testimony whereof, I have hereunto subscribed my name this 19th daydf April,

ORA COLBY.

risin solid an auxiliary 'Aresitbr granular material in said s-fliop- 110 

